First and foremost, be sure to use thinset mortar that is latex or polymer fortified; otherwise, it is likely to crack, resulting in loose tiles. You can buy bags of thinset mortar that are “polymer fortified” that you mix with water, or, you can buy less-expensive, unfortified thinset and add liquid latex as directed.

Use gray thinset for ceramic and stone tiles that are dark or deep in color. However, many types of marble, glass, and other kinds of tiles are slightly translucent, so a gray mortar would slightly muddy their color. For these tiles, use white thinset, which costs only a little more.

For most floor tiles, a square-notched trowel with ¼-inch notches produces grooves of the right thickness. For thicker tiles, larger notches may be recommended.

If the mortar starts to harden—either on the floor or in the bucket—while you work, throw it out and mix a new batch.

1) Mix the mortar. If you are tiling a medium- sized room, you can mix the mortar by hand. A margin trowel is the best tool for the job. Add a couple of inches of liquid to the bottom of a 5-gallon bucket and then pour in some powder. Stir with the trowel, scraping the bottoms and sides as you mix. Add the liquid slowly—it’s easy to add too much. Keep mixing until you attain a consistency that holds its shape and is barely pourable.

Mixing by hand is somewhat strenuous work; you must stir a heavy concoction briskly for a few minutes. If that is daunting, or if you have a large job, consider buying or renting a half-inch drill with a mixing paddle, which quickly and thoroughly mixes the mortar to a smooth consistency. Hold the bucket between your feet as you spin the paddle. Work slowly at first, to avoid slopping mortar out of the bucket. Then run the paddle until the mortar is smooth. When you pick the paddle up, the mortar should remain stuck for a few seconds before sliding off.

2) Spread the mortar. Dump or scoop the mortar onto the floor. Use the flat slide of the trowel to spread the mortar over an area about 3 feet square. Take care not to cover any layout lines.

3) Comb the mortar. Using the notched side of the trowel, comb the mortar to produce an even surface. Use long strokes and hold the trowel at a consistent angle.